This invention relates to a device for monitoring the temperature of cooled or deep-frozen products, such as foodstuffs, pharmaceuticals and the like, which device provides a permanent indication that a critical temperature has been exceeded.
Cooled or deep-frozen foodstuffs or other products may be preserved perfectly only if they are constantly and uninterruptedly kept below a critical temperature. In the case of cooled products, this temperature amounts to +8.degree. C., for example, and to -17.degree. C. for example in the case of deep-frozen products.
Even a brief heating action followed by refreezing may lead to serious deleterious changes to the products, e.g. foodstuffs, which frequently cause serious damage to health. Analogous remarks apply regarding pharmaceuticals, preserved blood and other products.
Strict monitoring of the "cooling chain" is required, particularly in the case of industrial chilling or freezing, until the defrosting operation prior to consumption of the foodstuffs.
Technical failures, as well as human oversights, are unfortunately never wholly preventable. The invention has as its object to specify a device which permits an uninterrupted verification that the specified critical temperatures had actually never been exceeded.
Until now, a monitoring operation on such cooled or deep-frozen products was only possible with difficulty. As a rule, use was made for this purpose of thermometers comprising following pointers, from which it was then possible to observe a rise above the critical temperature to the point of thawing of the cooled or deep-frozen product on the basis of the position of the following pointer. However, on the one hand such thermometers are comparatively costly and on the other hand, are easily manipulated.